A filtering and ventilating mechanism is driven by motors. The filtering mechanism rotates and presses downwards so its pressing surface is against a sample container. A ventilation needle is inserted into the sample container for ventilation. A mixing mechanism is arranged below the filtering mechanism and is driven by a mixing motor. The sample container is accommodated in a seat and is driven by the mixing motor. A test tube carrying mechanism is arranged below the mixing mechanism, and has an accommodating hole for a test tube. A jacking mechanism is arranged below the mixing mechanism, and is driven by a jacking motor. When the jacking mechanism moves upwards, a jacking platform is pressed against the bottom of the test tube, so that the test tube is butted against the bottom of the sample container, and a sample preparation in the sample container is dripped into the test tube.